Introduction. High intensity interval training (HIIT) has been proposed as effective means to increase aerobic capacity and insulin sensitivity in adults of different age (Gibala et al., 2012). The main aim of this study was to investigate acute physiological and psychological stress in response to three types of very low volume HIIT session in young (19.5 ± 1.3 years) and old (65.7 ± 2.8 years) women.

Results. Peak and average power were larger in young compared to old women and were largest during 6 × 5 strategy in both groups (p < 0.05). Both groups ranked 6 × 5 cycling as the most preferable for further training (90 %, p < 0.05). There was significant strategy and time interaction for P20 and P100 (p < 0.05). Strategy 6 × 5 did not change P100 in young, whereas in older group P100 was reduced only by 24 hours after 3 × 60 cycling (p < 0.05). P20/P100 ratio decline representing low frequency fatigue was more evident after 3 × 30 and 3 × 60 compared to 6 × 5 in both groups and was larger in young compared to old women (p < 0.05). Serum TNFα and IGF1 levels remained largely unchanged in both groups in response to any type of the three HIIT sessions.